Recently, with the active development of storage batteries, robots, satellites, and the like, along with the dramatically increasing demand for portable electronic products such as laptop computers, video cameras, mobile phones, and the like, research and development for high-performance secondary batteries capable of repeatedly charging and discharging has been actively made.
Currently, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, and the like are used as commercial secondary batteries. Among them, lithium secondary batteries have little to no memory effect in comparison with nickel-based secondary batteries, and thus lithium secondary batteries are gaining a lot of attention for their advantages of free charging/discharging, low self-discharging, and high energy density.
Particularly, with the steady exhaustion of carbon energy and increasing interest in the environment, the demand for hybrid vehicles and electric vehicles is recently gradually increasing all over the world including United States, Europe, Japan, and the Republic of Korea. Hybrid vehicles and electric vehicles are supplied with power for driving the vehicles from the charging/discharging energy of battery packs. Therefore, in comparison with vehicles powered by an engine alone, they have higher fuel efficiency and can eliminate or lessen the emission of pollutants, which adds to the appeal of hybrid vehicles and electric vehicles. Accordingly, research and development for vehicle batteries essential to hybrid vehicles and electric vehicles have intensified with gaining interest.
A battery not connected to an external power source such as an AC power are used in mobile devices such like a vehicle, which limits the available time of the battery. However, in the case that the available time of the battery is not properly predicted, a user may encounter great difficulties. For example, by improper prediction of the available time of the battery, a vehicle may stop in the middle of the road due to the battery discharging entirely.
In order to prevent the battery from abruptly discharging entirely due to the user not being able to properly predict the available time of the battery, a technique of estimating a residual capacity of the battery, namely the SOC (State Of Charge), and providing the information to a user is widely known in the art. The SOC of a battery generally represents a residual capacity as a percentage of FCC (Full Charge Capacity) of the battery. In order to estimate the SOC of a battery, various methods may be used; however, the most representative method is estimating the SOC by means of current integration. In the current integration, input/output currents of the battery are accumulated and added or subtracted to/from an initial capacity to obtain the SOC.
However, even if the SOC of a battery is estimated and provided to the user, the user may not accurately predict the available time of the battery. In other words, since the SOC represents a residual capacity to a user in the form of a percentage of the entire capacity of the battery, the user may not concretely determine the available time of the battery from the residual capacity information of the battery.
Particularly, even for batteries with the same SOC, depending on the habits and environments of the users, the available time of a battery may be different. For example, in the case of an electric vehicle, the available time of a battery may greatly vary depending on the driving habit of a user who frequently accelerates and abruptly brakes or the driving environment such as an uphill/downhill mountainous terrain.
However, according to the conventional technique, such situations are not considered at all, and in particular, a user may have difficulty predicting the accurate available time of a battery by just the SOC information.